1. Field of Use
This invention relates generally to combined steering and braking means for a crawler tractor or the like. In particular, it relates to a hydraulic control system having a combined steering and braking valve therein as well as other components.
2. Description of the Prior Art
In some prior art crawler tractors the hydraulic control system for the steering clutches and the track brakes includes a pair of manually operated steering clutch levers which actuate the valves for the steering clutches which transmit motive power from the tractor transmission to the tracks. A pair of brake pedals are used to selectively actuate a pair of brake cylinders which, in turn, control a pair of brakes for the tracks. Straight line vehicle movement is accomplished by engaging both clutches so as to drive both tracks in the same direction at the same speed. Steering is accomplished by operating one steering clutch lever so as to disengage its associated steering clutch and thereby slow down or stop its associated track while continuing to drive the other. Braking is accomplished during straight line vehicle movement by using both brake pedals and, during steering, by using the brake pedal for that track whose clutch is disengaged.
In such prior art tractors the steering clutches and the brake actuators are sometimes embodied in separate control systems which are supplied from separate hydraulic pumps. Aside from increased costs of such systems resulting from redundancy of components, such prior art systems often lack various automatic control functions which, if provided, would simplify and provide for safer tractor operation. The following patents disclose various types of prior art steering and braking control systems for vehicles: U.S. Pat. Nos. 3,437,184; 3,358,786; 3,386,523; 3,351,149; and 2,375,959.